Fibroadenomas are the most common benign tumors of the breast that usually affect premenopausal women but may occur at any age. Diagnosis of fibroadenoma rarely poses a diagnostic dilemma, even on core biopsy, FNA or frozen section. We presented here two rapidly growing infarcted fibroadenomas that were causing pain. Infarction within fibroadenoma is a very rare event and the frequency of infarction in our study is in line with a study of Haagensen
 who found only five infarcted cases among 1,000 reviewed breast fibroadenomas (rate: 0.5%). Another two studies based on the series of fibroadenomas in West African women revealed a slightly higher incidence of spontaneous infarction (0.9%)
[16, 17]. The highest frequency (3.6%) was reported in a recent study of Al-Atrooshi
The presence of infarction and necrosis are usually worrisome signs in breast pathology although spontaneous infarction can be seen in variety of benign breast lesions including fibroadenoma, phyllodes tumor, lactating adenoma, and intraductal papilloma
[3, 19–23]. Spontaneous infraction in fibroadenomas is a rare phenomenon and usually associated with pregnancy, lactation or a recent FNA
[5–7]. Exceptionally, spontaneous infarction may affect multiple fibroadenomas in the same patient
. Infarction may also be associated with the use of oral contraceptives
. Rarely, it can be seen in young patients without any associated risk factors, as illustrated in our two cases. The cause and mechanism of infarction are largely unknown. One of the possible explanations is that infarction represents a spectrum of regressive changes that also may include calcification and hyalinization, both of which are much more commonly seen in fibroadenomas
. Newman et al.
 also found thrombo-oclussive vascular changes as a possible cause of infarction within fibroadenomas.
In our first case, a focus of necrosis was seen on core biopsy which prompted excision biopsy while in the second case clinical suspicion for malignancy prompted an intra-operative frozen section consultation which also revealed the presence of intratumoral hemorrhage and necrosis. A meticulous histopathologic evaluation of the entire tumors, however, revealed no signs of malignancy despite the presence of necrosis. Of note, case #1 also showed areas of squamous metaplasia resembling so-called necrotizing syringometaplasia in the skin or sialometaplasia in salivary glands. This phenomenon has already been described in infarcted breast fibroadenomas
 and can also be seen in other benign breast lesions in a close proximity to the area of infarction (e.g. intraductal papilloma,
Fibroadenomas, particularly in older women, may be affected by various proliferative changes including malignant epithelial lesions
[29, 30]. The most frequent are in situ carcinomas (both ductal and lobular), and their invasive counterparts
[30–32]. Exceptionally, sarcomas may also develop within fibroadenomas (e.g. angiosarcoma, osteosarcoma)
[33, 34]. Little is known about the molecular mechanisms that drive the development and prog ression of malignant tumors within fibroadenomas. Comparative studies that analyzed various molecular markers in fibroadenomas and breast carcinomas failed however to identify the potential drivers
[35, 36]. However, a clonality study of Kuijper et al.
 indicated that fibroadenomas possessed a potential to progress in an epithelial direction (carcinoma) or in a stromal direction (phyllodes tumor).
We conclude that partial spontaneous infarction is a rare event in breast fibroadenomas and may not be associated with any known risk factor. The presence of necrosis on core biopsy or intra-operative frozen section should be cautiously interpreted and is not itself a sign of malignancy.